Oxygen is the most abundant element in nature. It forms approximately 21% of the atmosphere. It is bonded to hydrogen in water and it is found forming part of most minerals and rocks. It is a constituent of all living beings and is essential for ensuring the organic metabolism of animals. In superior vertebrates, such as man, oxygen is inhaled through the lungs and then subsequently transported through the bloodstream.
A basic life-supporting element, it is not surprising that oxygen is also essential in many medicinal applications. Many medical processes require this element as an agent to speed up metabolism. Oxygen therapy and air therapy are well known examples. Oxygen is also used in anesthesia, as well as in open heart surgery, where the patient's blood must be directly oxygenated. Oxygen, therefore, is may not be lacking in any hospital and is consumed in large amounts.
In order to ensure this supply and to enable its distribution throughout the hospital complex, a supply station typically distributes the product throughout the hospital through an internal distribution network. The supply station is usually composed of steel cylinders (bottles) which contain the gas under pressure. More recently, cryogenic tanks are used to store liquid oxygen at low temperature. After vaporization in a heat exchanger, the oxygen is supplied to the hospital network. All the stations have corresponding emergency systems, such as a set of bottles which act as a reserve and enter into operation in case of need should the main source suffer a serious breakdown or should there be no supply.
Medicinal oxygen is an expensive product whose price is determined by two factors. First, it is necessary that its purity be high, approximately 99.9%. It is also essential to ensure that oxygen for hospital consumption is not in any way polluted.
Second, consumption of the product by an average hospital is considerably smaller than in industrial consumption. The installations required for its storage, specifically in the case of cryogenic tanks, have similar and considerably higher costs, which have a more significant effect in the price of medicinal oxygen.
The medicinal application of pure oxygen is practically non-existent. In fact, pure oxygen is a highly toxic product and its continued inhalation causes death. It is therefore normally supplied with air or other gases in variable concentrations which very rarely exceed 80%. Most frequently, the oxygen product is provided in a proportion of around 40%. For this reason, American Pharmacopoeia has just authorized the classification of medicinal oxygen as oxygen which does not have an impurity of inert gases of over 7%, and therefore a concentration of oxygen equal to or over 93%.
The possibility of "filtering" air, separating its constituents, was achieved some years ago by means of zeolite filters or membranes, which absorb a gas (generally nitrogen) and allow the rest to pass through. Thus oxygen may be produced, in situ, with a considerably low cost by a system of compressors and filters. This requires reduced maintenance and low consumption of energy.
The main disadvantage of these units is that they cannot produce oxygen with a purity of over 95%. The need for such purity, however, has been eliminated with the recent authorization of American Pharmacopoeia. The required 93% purity is easily obtained with the main remaining impurity being the inert gas argon.
It is wholly unthinkable that a hospital may be deprived of the oxygen supply. This condition must be avoided at all costs and any supply system must absolutely prevent this. Autonomous generating units are not satisfactory because they are machines subject to possible breakdowns and stoppings.
By duplicating some parts of the system, it is possible to decrease the risk of stoppage, but, apart from the fact that total elimination of the risk thereof is impossible, successive accumulation of duplicate or safety elements make the costs of these units so high that the oxygen produced no longer has economic advantages.